Paper containing polyamide resins and process of producing same



United States Patent PAPER CONTAINING POLYAMIDE RESINS AND PROCESS OF PRODUCING SAME No Drawing. Application May 21, 1951, Serial No. 227,536

9 Claims. (Cl. 92-3) The present invention relates to a novel paper product and to the process of producing the same. More particularly it relates to the use of certain polyamide resin suspensoids as beater additives in the fabrication of paper. The invention involves the use of colloidally dispersed cationic aqueous suspensions of film-forming polyamide resin polymers. end additives and preferably are used without the addition of alum, size, or other commonly employed additives. The resultant products display improved wet strength, dry strength, and waterproofing properties.

Many beater additives or sizes or similar constituents for paper are known to the art. Most of these are added for only one specific purpose, such, for example, as waterproofing or wet strength development, or dry strength development, or filling for better ink receptivity,

and the like. In practically every case these additives must beused in conjunction with a precipitating agent which serves, first of all, to precipitate the additive from the dispersion in which they are usually added and'thereafter serves to fix the precipitated material to the fibers. The pulps which are used for the fabrication of paper are generally anionic in electrical charge because of the presence of carboxyl groups associated with the cellulose. If the sizes or other additives are also anionic-and this is very frequently the case-little retention to the fibers is observed unless a precipitating or electrical chargereversing agent such as aluminum sulfate is also employed.

It is known, of course, that beater additives or sizes can sometimes be made cationic to increase the retention by virtue of the attraction between the positive charge of the additive and the negative charge of the pulp. However, in order to prepare cationic dispersions for beater additives it has heretofore been necessary to employ an expensive cationic dispersing agent such as a quaternary ammonium salt, said cationic dispersing agent being wholly hydrophilic in character. These extrinsically dispersed materials will adhere to the pulp fibers and re tention in the heater is improved. Unfortunately, however, because of the hydrophilic nature of the dispersing agent, a wetting action is exerted with orientation at the water interface when the finished sheet is wetted. Thus penetration of the water into the sheet is fostered, and

additive, usually an acid salt which not only changes the character of the electrical charge of the mixture for paper retention but acts also as an acid catalyst to polymerize the formaldehyde complex to a water-insoluble fiber-to-resin bond in the presence of heat. In addition to the necessity for the use of large quantities of these additives, two other disadvantages are immediately ap- These dispersions are applied as wet- 2,767,089 Patented Oct. 16, 1956 parent. First of all, formaldehyde fumes are emitted, and these are a source of discomfort and actual toxicity. Accordingly, the use of formaldehyde-containing resins is to be avoided if possible. Secondly, even if these resin dispersions were made cationic in order to obtain the best retention on the fibers, this retention seldom exceeds one percent based on the dry weight of the pulp.

The disadvantages heretofore described are overcome in the present invention because the materials employed are suificiently cationic so as to be markedly attracted to the anionic pulp fibers, and accordingly no co-precipitant is needed. 1 As a matter of fact, the use of a co-precipitant is ordinarily undesirable. Furthermore, the material has been made cationic by the use of intrinsic emulsifiersthat is, the emulsifying entities are in themselves part of the resin. Thus the extrinsic, hydrophilic, cationic emulsifiers previously used are eliminated. Since the emulsifiers are part of the resin, the orientation at a water interface, as demonstrated by an ordinary cationic emulsi fier, is practically eliminated since the emulsifying portion is bound to the resin and is not free to orient at will. Because of this the desirable effects of a cationic additive are achieved without in any way impairing the waterproofness of the final paper. Moreover, the products described in this invention need not be used in excessively high proportion unless certain specific results inherent in the use of large quantities of the material are desired. In addition, the materials employed are innocuous, and there is no need for noxious materials such as formaldehyde. Finally, the materials described in this invention provide an exceptionally high degree of wet strength, a high degree of dry bonding strength and a high degree of waterproofness. Furthermore, the degree of retention exhibited by the materials contemplated within the present invention on the pulp fibers is excellent.

It is therefore an object of the present invention to provide novel paper products containing as beater additives polyamide suspensoids which provide continuous films.

It is another object of the present invention to provide a novel process of producing such paper products.

The cationically dispersed polyamide suspensoids capable of forming continuous films which may be employed in the present invention are those described in the copending application of Harold Wittcoff and Wesley A. Jordan entitled Polyamide Suspensoids Forming Continuous Films, Serial Number 227,535, filed May 21, 1951, now abandoned. These suspensoids are prepared by the dispersion in an acidic aqueous medium of a polyamide derived from polymeric fat acids and polyamines having at least 3 atoms intervening between the amine groups principally involved in the amidification reaction, the polyamide having an amine number of at least 5. The polymeric fat acids employed may be those resulting from the polymerization of drying or semi-drying oils,

or the free acids or simple aliphatic alcohol esters thereof. Suitable drying or semi-drying oils include soybean,

linseed, tung, perilla, oiticica, cottonseed, corn, tall, sunflower, safilower, dehydrated castor oil, and the like. In'

the polymerization process for the preparation of the polymeric fat acids, the fatty acids with sufiicient double bond functionality combine, for the most part, probably by a Diels-Alder mechanism to provide a mixture of dibasic and higher polymeric acids. The acids with insufficient functionality to react remain as monomers and may be removed by distillation. The residue after distillation consists of the desired polymeric acids, and this mixture is used for the preparation of the polyamide resin. In place of this method of polymerization, any other method of polymerization may be employed, whether the resultant polymer possesses residual unsaturation or not. The term polymeric fat acid as used herein is intended to include The polyamines which may be employed forv the prep-n aration of the polyarnides are those in which the amine groups which are principally involvedin the amidificationreaction are separated by at least three atoms. These three atoms may be carbon atoms or hetero atoms. Type ical of the polyamines which may be used are diethylene triamine, triethylene tetrarnine, tetraethylene pentamine, 1, 4-d iamine butane, 1,3-diamino butane, hexamethylene diamine, diacetone diamine, B-(N-isopropylamino) propylamine, 3,3-iminobispropylamine, and the like. It. Will be observed that in the case of the fi rst three named poly: amines, there, are amine groups which are separatedby only two carbon atoms. However, the amidification. rectio involves he P ma y amine sl psp inc pally, n

the product obtained is suitable for. the purposesof, the; present'invention. It is also apparent that some of: the polyamines contain only a single primzuryv amine group and in addition a secondary amine gropp, Undert-hese circumstances the secondary amine group also, bfiCQmes involved in the amidification reaction to a large extent whereas in the case of diethylene triamine, for example, are two primary amine groups are amidified to the virtual exclusion of the secondary amine gropp. From the above discussion it is apparent that a wide variety of polyam ines maybe employed as long as the amine groups primarily involved in the amidification reaction are sep ara ted at least 3 atoms.

In the preparation o f the polyamide the polymeric fat aeids are reacted with any of the polyamines referred to above, either singly or in admixture. The final polyarnide obtained, musthave some free amine groups, the relative number of which is referred to as the amine number. As used herein amine number means the milligrams of KOH equivalent to the free amine groups in one gram of the'product. Preferably this amine number should be at. least 5, and preferably is at least 10. Amine numbers may be as high as 100 or more. This amine number may be theresult of the employment of the polyamine in excess or' as a result of only partial reaction of the polyaminewhich is employed. Thus in the case of diethylene triarnine, triethylene tetramine and tetraethylene pentarnine, i't is usually preferred to employ the polyamide in a. quantity such that the primary arnine groups are ap-. proximately equivalent to the carboxylgroups in the polymeric fatacids including the carboxyls in the polybasic acids as well 'as the, carboxyl groups in any monomer which may be present. When these proportions are employed, the reaction between the carboxylgroups and the polyamines involves almost entirely the primary amine groups, and thefsecondary amine groups remain as free amine groups in the polymer. Where less polyamine is employed than that is equivalent in primary amine groups to the carboxyl groups, some of the secondary amine groups may rea'ctwi'th the carboxyl groups. and

there is the possibility of obtaining cross-linked polymers Which would have a ten dency to gel. Accordingly it is preferred notto involve the. secondary amine group sin the am de-formmg reaction where such polyamines; as

diejthylene triamine, triethylene tetrarnine, and "tetraethylw ene pentamine are employed. Too large an excess of mupssmu'm be; avoided inasmuch as this tends ucje the size, of thepolymer to the. point where the.

pi' o'd ct might not possess. the desired physical character,

is tics "In. general, amine numbers between Sand 100 are satisfactory, and those skilled in the art can readily deter mine the particular proportions of amine and polymeric fat acids to be employed'for theproduction of a polymer having the desired characteristics. 7 H

.Polyamides, of this type generally have molecular;

weights varying from 1' ,0 O to 10,000, and are resistant to, the: corrosive action ofwater, alkali, oils, greases, and

organic solvents. The melting points vary depending upon the reactants and the reaction conditions. These melting points may vary from about 25 C. to C. They vary in degrees of hardness, depending upon the melting point, but in general, all are tacky resins. Some resins of this type have been disclosed in Cowan et al. Patent No. 2,450,940, and such resins are useful in the present invention.

In preparing a suspensoid from these polyamides, the polyam'ide is simply melted and then poured into water containing a small amount of acid while the mixture is being agitated. The mixture is heated and stirred and as a result dispersion of the polyamide readily occurs. A wide variety of acidsmay be employed in the aqueous phase. Suitable acids include formic, acetic, propionic, butyric, monochloracetic, hydrochloric, phosphoric, boric, fumaric, lactic, maleic, oxalic, tartaric, glycolic, benzoic, succinic, terephthalic, furoic, and gallic acids. Only a small quantity of acid is necessary to effect the dispersion. The quantity of acid is only a small portion of that which would be required to neutralize free amine groups in the polymer where the polymer has an amine number of 20. or more. In the case of polymers having amine numbers below 20 a substantial portion of the amine groups should be neutralized. Polymers having amine numbers below 10 would require substantially complete neutralizationof the amine groups. For example, with diethylene triamine resins sufficient acid is employed to neutralize amine'groups equivalent to an amine number of about 7 to. 15. The optimum quantity of acid for any particular pplyamide varies with the resin and can readily be determined by trial. When larger quantities of acid are employed, colloidal solutions or gels may be. formed, especially where the amine number is above 20. These are useful in some applications, but in general, are less desirable than the suspensoids which are preferred. This phenomenon, however, may be made use of in controlling the viscosity of the suspcnsoid, particularly in the case of polya nides of high amine number.

The. solids concentrations, in these suspensoids can be varied widely. Preferred compositions frequently have solids concentrations in the range of 35-60%. Higher and: lower concentrations are, of course, possible and extreme. dilutions are feasible. The particle size in these suspensoids isof the order of 1 micron.

During the preparation of these suspensoids, itis possible to incorporate other ordinarily non-dispersible reagents into the reaction mixture. These include waxes such as parafiin Wax, rosin, rosin esters, and a great variety of other resinous materials such as phenol-formalder hyde resins, acrylic polymers, vinyl polymers of many kinds, urea formaldehyde, melamine polymers, and the like. The. incorporation of additives of this nature in small quantities, especially material such asparaflin wax or-antioxidants, has; been found to be advantageous from necessaryto addthe suspensoid to the pulp, after Whichthe. pulp is-well agitated and the paperismanufactured in the conventional way. The pulps which maybe-used include bleached sulfite pulps, reclaimed paper, liraft pulps, ground Wood'pulp, neutral'sulfite pulps, soda pulps',

and fact any type of wood pulp, straw, rags, or other pulp material of cellulosic origin,

In general the concentration of the suspensoids contemplated inlthepresent invention may vary. from 1% to 20%, as suspensoid solids based on the dry weight of, the pulp fibers. In general, however, it is preferred. to op;

era tewithin the range of-3% to 6%. It is advantageous to heat treat and/ or calender-the paper after it, has been fabrieated, aswill be shown in the examples,

points; of view as will be detailed below in the memes I 6 Example 1 A polyamide was prepared from a polymeric fat acid having the following composition:

Forty pounds of this polymeric fat acid, 2.4 pounds of cottonseed fatty acids, and 7.48 pounds of a 95.6% aqueous solution of diethylene triamine were heated with stirring to 200 C. Heating was effected slowly since a tendency toward foaming was observed. After the temperature reached 200 C. it was maintained there for 3 hours with vigorous agitation, and during the last hour vacuum was employed. At the end of the reaction period the vacuum was released and the product was cooled. The reaction mixture was maintained under an inert gas blanket during all the time at which it was at an elevated temperature with the exception of the time during which the vacuum was employed. The product had the following properties:

Melting point (ball and ring) C 46.0-46.5 Color 1 (Gardner) -11 Viscosity 1 at 25 C. (Gardner-Holdt) B-C Acid number 5.2 Amine number 86 Determinations carried out on 35% solutions in butanoltoluene (1 1).

To 32.3 pounds of the above resin heated to 160 C. there was added with vigorous stirring 32.3 pounds of hot water containing 0.26 pounds of acetic acid. After agitation for one hour, there resulted an extremely smooth dispersion, which provided a continuous tacky film. The suspensoid demonstrated the following properties:

Percent solids 52.1 Acid number 6.0, 6.1 Amine number 43.2, 43.8 pH 7.6

This suspensoid was added directly to a bleached sulfite pulp in the beater at the rate of 3% suspensoid solids based on the weight of the dry fiber. The usual rosin size and alum were omitted. The sheet was formed in a normal way and after the normal drying it was cured for from 10 to minutes by heating at 240-280 F. The product obtained had a wet strength over 6 times the wet strength of an untreated sheet when both were wetted with a dilute solution of a wetting agent such as sodium lauryl sulfate. The product demonstrated a bursting and tensile strength of 1.4 times that of the untreated sheet, and a water resistance as measured by TAPPI standard T433M-44 dry indicator method of at least that attained by 3% rosin size and alum to pH 4.5 to 5.0 These results are indicated in the following table:

Example 2 349.3 parts of the polymeric fat acid of Example 1 and 116.8 parts of triethylene tetramine were heated with stirring to 200 C. The heating period required about 2 hours, during which time the vapor temperature was never allowed to exceed 99 C. The reaction mixture was then maintained with stirring at200 C. for 3 hours, and dur: ing the last hour vacuum was employed. Thereafter the product was cooled. Again an inert atmosphere was employed while the product was at an elevated temperature. The product had the following properties:

Melting point (ball and ring) ..C 27-28 Color (Gardner) i 8-9 Viscosity at 25 C. (Gardner-Holdt) A1 Acid number 3.4 Amine number- 177.0

Five hundred parts of the resin were heated to 150 C. and to the heated resin were added 930 parts of water containing 4 parts of glacial acetic acid, the water having been heated first to C. After the addition vigorous stirring was employed for approximately one-half- Wet TAPPI-t Sheet containing as Beater additive tensile T433-M4 Strength Size Test Grams Seconds 3% resin suspensoid solids as described in Example 2 377 36 6% resin suspensoid solids as described in Examp 2 403 36 Blank sheet, no additive 1 Example 3 A comparison was made between the papers obtained by the employment of the polyamide suspensoidsof the present invention and papers obtained using urea-formaldehyde resins as additives. The suspensoid employed was that described in Example 1. For comparison pur poses a so-called urea-formaldehyde stage resin was employed. This material was a partially polymerized urea-formaldehyde resin which had not yet reached the insoluble and infusible stage. The resin was employed in the form of a cationic solution and was characteristic of urea-formaldehyde resins employed for this purpose in the paper industry. The papers produced were heat treated in the manner set forth in the preceding examples. This heat treatment is particularly important in the case of the urea-formaldehyde resins in order to set such resins. The superior results obtained-by the employment of the polyamide suspensoid are indicated in the following table: I

Example 4 The effect of varying concentrations of suspensoid on the resultant paper are indicated by the present example in which a series of papers were formed from the same paper pulp to which increasing increments of polyamide suspensoid were added as a heater additive. The sheets were finished and heat treated as described in Example 2.

The effect of varying time-periods of heat treatment is demonstrated in the present example which a series of papers wereprepared, all containing3% of suspensoid solids basedon the dry weight of thefiber. These suspensoids were again added as the solebeater additive and thepapers were-made and heat treated for varying times on an electrically heated-drier witha surface temperature of 238 F. For comparison purposes one sheet was airdried and a blank sheet containing no polyarnide suspensoid was dried for 6 minutes at 238 F. The results are indicated in the following table:

Heating Wet TAPPI Percent Polyamide Resin suspensoid Time at Tensile T433-M44 238 F. Strength Size test Min. G. Sec. Blank sheet 6 113 1 3 o Resin (sheet air-dried). 187 l4 3 n Resin 3 257 16 D 6 327 22 9 487 37 12 470 48 15 490 75 20 570 58 30 720 63 Example 6 Paraffin wax was employed in conjunction with the polyamide resin suspensoid. For this purpose the resin described in Example 1 was used. The suspensoid was prepared in the following manner: To a melt of 10-0 parts of thepolyamide resin and parts of parafiin wax (melting point 135-137 F.) heated to 140 C., was added with rapid agitation a hot (90 C.) solution of 1.6 parts of acetic acid and 185 parts of water. Vigorous agitation gave a smooth dispersion which provided a continuous tacky film. The product had a solids content of 36% and apH of 8.8

.A series ofpaper sheets were made from this mixed suspensoid of polyamide and wax and compared with sheets made from the polyamide suspensoid in Example 1. These sheets were heat treated as previously described atthe temperaturesand for the time periods indicated. It willgbeseen from the following table that the paraflincontaining suspensoid provides a more water resistant sheet at moderate curing temperatures than does the resin alone even at higher curing temperatures. In addition, the 'wet strength of such sheets is improved by the presence of a paraffin.

Wet TAPPI 'BeaterAdditlve 'lemperature and Tensile T433-M44 Time of drying Strength, Size Test,

g. sec.

238 1*., 12'min 667 i 08 288 F., 12 min +900 98 238 F., 6 min 440 40 250 F., 12 min 517 49 250 F., 20 min 480 51 260 F., 12 min. 570 49 260 F., 20 min 567 79 250 F., 12 min 613 52 250 F., 20 IN 678 62 597 51 760 48 Other waxes such as microcrystalline wax, montan wax, ,carnauba'wax, and the like, can also be used. Parafin wax, however, is preferable because of its low price and availability. The ratio of waxes to resin solids may also be varie'dabove and-below the'five percentlevel demonstrated here, but for the most part, the preferred results are obtained with 5%. Other co-additives may also be used in the suspensoid such as latex emulsions, stabilizers, and certain gums.

We claim as our invention: 7

1. A cellulosic paper product comprising fibers having dispersed among the fibers thereof a .polyamide having the polyacyl group of polymeric fat acids, and the polyamino group of an aliphatic polyamine, the amino groups primarily involved in the polyamide formation being separated by at least 3 atoms, the polyarnide having a molecular weight within the approximate range of 1,000 to 10,000, said polyamide having an amine number'of at least 5.

2. A cellulosic paper product comprising fibers hav ing dispersed among the fibers thereof a polyamide having'the polyacyl group ofpolymeric fat acids, and the polyamino group of an aliphatic polyamine, the amino groups primarily involved in the polyamide formation being'separated 'by at least 3 atoms, the polyamide having a molecular weight within'the approximate range or 1,000 to 10,000, said polyamicle having an amine number offrom li) to 100.

3. ProducLaccording-to.claim 1 in which the polyamine used -inpreparing the polyamide is cliethy-lene triamine.

4. Product according-to claim 1 inwhichtheipolyamine used to prepare the polyamide is triethylene tetramine.

5. Process ofproducing cellulosic paper products which comprises adding torpaperpulp as a better additive a suspensoid in an aqueous medium of a polyamide having the p'olyacyl group of polymeric fat acids, and the polyaminogroup of an aliphatic polyamine, the amino groups primarily involved in the polyarnide formation being separated by at least 3 atoms, the polyamide having a molecular weight within the approximate range of 1,000 to 10,000, said polyamide having an amine number of at least 5 and being dispersed in an aqueous medium by means of sufficient acid to produce a stable suspensoid, said suspensoid being capable of forming continuous tacky films, and converting said pulp into a paper product.

6. Process according to claim 5 in which the polyamine employed forthe preparation of the polyarnide is diethylene triamine.

7. Process according to claim 5 in which the polyamine employed for the preparation of the polyarnide is triethylene tetramine.

'8. Process according to claim 5 in which the polyamide is employed in the quantity of from 3% to 6% calculated as suspensoid solids and based on the dry weight of the fiber in the pulp.

9. Process according to claim 5 in which the paper product after formation is cured'at temperatures Within the range of 230 F. to 280 F. for a time period within the approximate range of 3 to 20 minutes.

References Cited in the file of this patent UNITED STATES PATENTS (Other references on following page) 10 FOREIGN PATENTS Cowan et 211.: Oil and Soap, vol. 21, pp. 101-107, 46,505 0 1 A .22,1950 APri11944- 7 ana a ug Polyamide Resin Suspensoids by General Mills, Inc.

OTHER REFERENCES Oct. 20, 1950, pp. 1-16. (Pubs. in Div. 50..) Maxwell: Paper Trade 1. May 13, 1943 (page 41). 5 Collins: Paper Ind. & Paper World, June 1943, pp. 263-269. (Both publications in Science Library.) 

1. A CELLULOSIC PAPER PRODUCT COMPRISING FIBERS HAVING DISPERSED AMONG THE FIBES THEREOF A POLYAMIDE HAVING THE POLYACYL GROUP OF POLYMERIC FAT ACIDS, AND THE POLYAMINO GROUP OF AN ALIPHATIC POLYAMINE, THE AMINO GROUPS PRIMARILY INVOLVED IN THE POLYAMIDE FORMATION BEING SEPARATED BY AT LEAST 3 ATOMS, THE POLYAMIDE HAVING A MOLECULAR WEIGHT WITHIN THE APPROXIMATE RANGE OF 1,000 TO 10,000, SAID POLYAMIDE HAVING AN AMINE NUMBER OF AT LEAST
 5. 